1. Field of the Invention
The present invention relates generally to an electric power source for a motor vehicle and, in particular, to an electric power source for a motor vehicle, in which a voltage outputted from a battery is shut off when an interlock wire is in a disconnected state.
2. Description of the Related Art
FIG. 1 is a circuit diagram showing a background art electric power source for a motor vehicle. The power source has a battery 31 of its own connected via an output connector 41 to a vehicle side. In this power source, when the output connector 41 is detached, an output terminal 46 of the power source becomes exposed to the outside. Since the output terminal 46 remains connected to the battery 31 which produces a high-voltage direct current, there is a contactor 32 provided for shutting off a power supplied from the electric source in order to prevent an operator or user from getting an electric shock while the output connector 41 is detached. An interlock circuit 33 is provided in order to turn off the contactor 32 while the output connector 41 is detached. The interlock circuit 33 is adapted to turn off the contactor 32 when a disconnected state is detected of an interlock wire 34 which is provided to the output connector 41. This is possible because when the output connector 41 is detached, the interlock wire 34 also comes to a disconnected state.
The shown power source is also provided with an interlock switch 44 that is connected in series to the battery 31. The interlock switch 44 serves to enhance safety and security by shutting off a voltage outputted from the power source, like when the power source is being repaired. The interlock switch 44 is manually operated like when the power source is repaired, or the switch is turned off from its “on” state when it is detected that a casing is opened. The power source with such interlock switch 44 facilitates maintenance to be carried out safely by breaking an output circuit. This power source has a detection switch 45, connected in series to the interlock wire 34, for detecting an on-and-off state of the interlock switch 44, so that when the interlock switch 44 is turned off, the contactor 32 connected to the output side of the battery 31 is turned off for enhanced safety. There has certainly been developed a power source having interlock switch connected in series to battery as described above (refer to Japanese Laid-Open Patent Publication No. 2004-1652).